${\text{Cu}}_{0.5}{\text{Co}}_{0.5}{\text{Cl}}_{2}{\text{-FeCl}}_{3}$ graphite bi-intercalation compound is a three-dimensional short-range spin glass with a spin freezing temperature ${T}_{\text{SG}}$ $(=3.92\ifmmode\pm\else\textpm\fi{}0.11\text{ }\text{K})$. The time evolution of the zero-field-cooled magnetization ${M}_{\text{ZFC}}(t)$ has been measured under various combinations of wait time $({t}_{w})$, temperature $(T)$, temperature shift $(\ensuremath{\Delta}T)$, and magnetic field $(H)$. The relaxation rate ${S}_{\text{ZFC}}(t)$ $[=(1/H)d{M}_{\text{ZFC}}(t)/d\text{ }\text{ln}\text{ }t]$ shows a peak at a peak time ${t}_{\text{cr}}$. The shape of ${S}_{\text{ZFC}}(t)$ in the vicinity of ${t}_{\text{cr}}$ is well described by stretched exponential relaxation (SER). The SER exponent $b$ and the SER relaxation time ${\ensuremath{\tau}}_{\text{SER}}$ are determined as a function of ${t}_{w}$, $T$, $H$, and $\ensuremath{\Delta}T$. The value of $b$ at $T={T}_{\text{SG}}$ is nearly equal to 0.3. There is a correlation between ${\ensuremath{\tau}}_{\text{SER}}$ and $1/b$, irrespective of the values of ${t}_{w}$, $T$, $H$, and $\ensuremath{\Delta}T$. These features can be well explained in terms of a simple relaxation model for glassy dynamics.